This invention relates to organophotoreceptors suitable for use in electrophotography and, more specifically, to flexible organophotoreceptors having novel charge transport compounds comprising a diformylcarbazole bishydrazone group.
In electrophotography, an organophotoreceptor in the form of a plate, disk, sheet, belt, drum or the like having an electrically insulating photoconductive element on an electrically conductive substrate is imaged by first uniformly electrostatically charging the surface of the photoconductive layer, and then exposing the charged surface to a pattern of light. The light exposure selectively dissipates the charge in the illuminated areas, thereby forming a pattern of charged and uncharged areas. A liquid or solid toner is then deposited in either the charged or uncharged areas depending on the properties of the toner to create a toner image on the surface of the photoconductive layer. The resulting toner image can be transferred to a suitable receiving surface such as paper. The imaging process can be repeated many times to complete a single image and/or to reproduce additional images.
Both single layer and multilayer photoconductive elements have been used. In single layer embodiments, a charge transport material and charge generating material are combined with a polymeric binder and then deposited on the electrically conductive substrate. In multilayer embodiments, the charge transport material and charge generating material are in the form of separate layers, each of which can optionally be combined with a polymeric binder, deposited on the electrically conductive substrate. Two arrangements are possible. In one arrangement (the xe2x80x9cdual layerxe2x80x9d arrangement), the charge generating layer is deposited on the electrically conductive substrate and the charge transport layer is deposited on top of the charge generating layer. In an alternate arrangement (the xe2x80x9cinverted dual layerxe2x80x9d arrangement), the order of the charge transport layer and charge generating layer is reversed.
In both the single and multilayer photoconductive elements, the purpose of the charge generating material is to generate charge carriers (i.e., holes and/or electrons) upon exposure to light. The purpose of the charge transport compound is to accept at least one type of these charge carriers, generally holes, and transport them through the charge transport layer in order to facilitate discharge of a surface charge on the photoconductive element.
In a first aspect, the invention features an organophotoreceptor that includes:
(a) a charge transport compound having the formula: 
where R1 is hydrogen, a branched or linear alkyl group (e.g., a C1-C30 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, or an aryl group (e.g., a phenyl or naphthyl group); and
R2 and R3 independently have a structure of: 
in which Ar is selected form the group consisting of; 
R4 is a hydrogen, or an aromatic group;
(b) a charge generating compound; and
(c) an electrically conductive substrate.
In a second aspect, the invention features an electrophotographic imaging apparatus that includes (a) a plurality of support rollers; and (b) the above-described organophotoreceptor operably connected to the support rollers with motion of the support rollers resulting in motion of the organophotoreceptor. The apparatus can further include, for example, a liquid toner dispenser, although dry toner can also be used with the organophotoreceptor.
In a third aspect, the invention features an electrophotographic imaging process that includes (a) applying an electrical charge to a surface of the above-described organophotoreceptor; (b) imagewise exposing the surface of the organophotoreceptor to radiation to dissipate charge in selected areas and thereby form a pattern of charged and uncharged areas on the surface; (c) contacting the surface with a toner, such as a liquid toner that includes a dispersion of colorant particles in an organic liquid, to create a toned image; and (d) transferring the toned image to a substrate.
In a fourth aspect, the invention features a novel charge transport material having the formula
(a) a charge transport compound having the formula: 
where R1 is hydrogen, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, or an aryl group (e.g., a phenyl or naphthyl group); and
R2 and R3 independently have a structure of: 
in which Ar is selected form the group consisting of; 
R4 is a hydrogen, or an aromatic group.
These photoreceptors can be used successfully with liquid toners to produce high quality images. The high quality of the images can be maintained after repeated cycling.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.